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Simple Summary: Hybrid rice often has higher yields than comparable inbred varieties. However, hybrids are sometimes more susceptible to insect herbivores. Outbreeding can improve herbivore resistance in hybrids compared to one (a condition called heterosis) or both (called heterobeltiosis) of their parental lines. The frequency of heterosis for resistance has not been assessed under varying soil nitrogen conditions. Nitrogen is predicted to reduce a plant's ability to resist herbivores but increases its ability to compensate for damage, known as tolerance. We examined the resistance and tolerance of eight hybrids and their parental lines to herbivores by exposing plants to the brown planthopper, whitebacked planthopper or yellow stemborer and observing herbivore fitness responses (i.e., resistance) and herbivore-induced changes to plant biomass (i.e., tolerance). There were no consistent trends in relative resistance or tolerance to the herbivores across plant types; however, improved resistance and tolerance were frequently associated with the male parent. Nitrogen reduced resistance and generally increased tolerance to herbivores irrespective of plant type. Across the eight hybrids, relative resistance and relative tolerance were not determined by heterosis or heterobeltiosis. Our results highlight the difficulties in predicting the outcomes of crossing to achieve relatively resistant hybrids. Hybrid rice results from crossing a male-sterile line (the A line) with a pollen doner (the restorer or R line). In 3-line hybrid breeding systems, a fertile B line is also required to maintain A line populations. Heterosis is defined as a condition of traits whereby the hybrid exceeds the average of the parental lines. Heterobeltiosis is where the hybrid exceeds both parents. Hybrid rice may display heterosis/heterobeltiosis for growth, yield and resistance to herbivores, among other traits. In a greenhouse experiment, we assessed the frequency of heterosis for resistance to the brown planthopper (Nilaparvata lugans (BPH)), whitebacked planthopper (Sogatella furcifera (WBPH)) and yellow stemborer (Scirpophaga incertulas (YSB)) in eight hybrids under varying soil nitrogen conditions. We also assessed plant biomass losses due to herbivore feeding as an approximation of tolerance (the plant's capacity to compensate for damage). Nitrogen reduced resistance to all three herbivores but was also associated with tolerance to WBPH and YSB based on improved plant survival, growth and/or yields. Plant biomass losses per unit weight of WBPH also declined under high nitrogen conditions for a number of hybrids, and there were several cases of overcompensation in rice for attacks by this herbivore. There was one case of nitrogen-related tolerance to BPH (increased grain yield) for a hybrid line with relatively high resistance, likely due to quantitative traits. Heterosis and heterobeltiosis were not essential to produce relatively high herbivore resistance or tolerance across hybrids. [ABSTRACT FROM AUTHOR]

Simple Summary: Hybrid rice is produced by crossing a male sterile rice line (the A line) with a pollen doner that restores fertility (the restorer line). The consequential outbreeding can result in plant growth and yields that are above the average of the parental lines (a condition called heterosis). This gives rise to a normally higher productivity of hybrids compared to pure-line (inbred) rice varieties. However, hybrid rice has also been associated with higher herbivore damage compared to inbreds. In particular, susceptibility to the whitebacked planthopper (Sogatella furcifera) has been linked to the A line in early generation hybrids. We tested whether hybrids had heterosis for resistance to the whitebacked planthopper, brown planthopper (Nilaparvata lugens) and yellow stemborer (Scirpophaga incertulas) in a series of greenhouse and field experiments. In the field plots, heterosis resulted in relatively high hybrid yields. There were few cases of heterosis for resistance to herbivores in the greenhouse or field and only one of eight A lines was associated with susceptibility to planthoppers. Susceptibility to the yellow stemborer was largely due to plant physiology: larger, fast-growing and late-maturing varieties, including hybrids, were more vulnerable to stemborers. Therefore, susceptibility to stemborers was often a consequence of heterosis for plant biomass. We make a series of recommendations to improve screening and breeding for resistance to herbivores in hybrid rice. Three-line hybrid rice is produced by crossing male sterile (A line) rice with a fertility-restorer (R line). Fertile lines (B lines) are also required to maintain A line seed for breeding programs. We used a range of hybrids and their parental lines to assess the frequency and nature of heterosis for resistance to the whitebacked planthopper (Sogatella furcifera), brown planthopper (Nilaparvata lugens) and yellow stemborer (Scirpophaga incertulas). Heterosis is defined as trait improvement above the average of the parental lines as a result of outbreeding. Based on the results from a greenhouse study that challenged hybrids and their parental lines with each herbivore species, we found that susceptibility to planthoppers was associated with one of the eight A lines tested, but resistance was improved by crossing with a relatively resistant restorer. Higher frequencies of heterosis for susceptibility in comparisons between hybrids and their B lines suggest that susceptibility was not related to the cytoplasmic genomes of the associated sterile A lines. Furthermore, because none of the parental lines possessed currently effective resistance genes, improved resistance against planthoppers was probably due to quantitative resistance. In a related field trial, hybrids had generally higher yields than their fertile parents and often produced larger grain; however, they were often more susceptible to stemborers, leaffolders (Cnaphalocrocis medinalis) and other caterpillars (Rivula atimeta). This was largely a consequence of hybrid heterosis for plant biomass and was strongly affected by crop duration. We make a series of recommendations to improve hybrid breeding to reduce the risks of herbivore damage. [ABSTRACT FROM AUTHOR]

Plant–ungulate interactions are critical in shaping the structure of Mediterranean plant communities. Nevertheless, there is a dearth of knowledge on how plant intrinsic and extrinsic factors mediate the sign and strength of plant–ungulate interactions. This is most relevant when addressing natural or assisted restoration of plant communities in human‐disturbed areas.We conducted field‐clipping experiments simulating how different intensities of ungulate herbivory may affect the natural regeneration and establishment of the Mediterranean dwarf palm (Chamaerops humilis), a keystone species in Mediterranean ecosystems. We quantified seedling survival and size in two human‐disturbed sites (SW Spain) where wild and domestic ungulates exert high herbivory pressure on vegetation.Severe clipping and seedling aging reduced rates of seedling survival. In contrast, moderate clipping did not affect seedling survival, suggesting a certain degree of C. humilis tolerance to herbivory. Severe clipping reduced seedling height strongly but not seedling diameter, and these effects seem to have decreased seedling survival. Nurse shrubs increased seedling size, which likely improved seedling survival. We also found seedling compensatory growth which varied between study sites.Field‐clipping experiments can help disentangle effects of plant extrinsic and intrinsic factors on the sign and strength of plant–ungulate interactions and their ecological consequences on the dynamics of human‐disturbed ecosystems. We call attention to the importance of appropriately managing scenarios of severe herbivory and summer droughts, particularly frequent in Mediterranean ecosystems, as synergic effects of such key drivers can negatively affect the structure and dynamics of plant communities and endanger their conservation. [ABSTRACT FROM AUTHOR]

Hybrid rice results from crossing a male-sterile line (the A line) with a pollen doner (the restorer or R line). In 3-line hybrid breeding systems, a fertile B line is also required to maintain A line populations. Heterosis is defined as a condition of traits whereby the hybrid exceeds the average of the parental lines. Heterobeltiosis is where the hybrid exceeds both parents. Hybrid rice may display heterosis/heterobeltiosis for growth, yield and resistance to herbivores, among other traits. In a greenhouse experiment, we assessed the frequency of heterosis for resistance to the brown planthopper (Nilaparvata lugans (BPH)), whitebacked planthopper (Sogatella furcifera (WBPH)) and yellow stemborer (Scirpophaga incertulas (YSB)) in eight hybrids under varying soil nitrogen conditions. We also assessed plant biomass losses due to herbivore feeding as an approximation of tolerance (the plant’s capacity to compensate for damage). Nitrogen reduced resistance to all three herbivores but was also associated with tolerance to WBPH and YSB based on improved plant survival, growth and/or yields. Plant biomass losses per unit weight of WBPH also declined under high nitrogen conditions for a number of hybrids, and there were several cases of overcompensation in rice for attacks by this herbivore. There was one case of nitrogen-related tolerance to BPH (increased grain yield) for a hybrid line with relatively high resistance, likely due to quantitative traits. Heterosis and heterobeltiosis were not essential to produce relatively high herbivore resistance or tolerance across hybrids.

Three-line hybrid rice is produced by crossing male sterile (A line) rice with a fertility-restorer (R line). Fertile lines (B lines) are also required to maintain A line seed for breeding programs. We used a range of hybrids and their parental lines to assess the frequency and nature of heterosis for resistance to the whitebacked planthopper (Sogatella furcifera), brown planthopper (Nilaparvata lugens) and yellow stemborer (Scirpophaga incertulas). Heterosis is defined as trait improvement above the average of the parental lines as a result of outbreeding. Based on the results from a greenhouse study that challenged hybrids and their parental lines with each herbivore species, we found that susceptibility to planthoppers was associated with one of the eight A lines tested, but resistance was improved by crossing with a relatively resistant restorer. Higher frequencies of heterosis for susceptibility in comparisons between hybrids and their B lines suggest that susceptibility was not related to the cytoplasmic genomes of the associated sterile A lines. Furthermore, because none of the parental lines possessed currently effective resistance genes, improved resistance against planthoppers was probably due to quantitative resistance. In a related field trial, hybrids had generally higher yields than their fertile parents and often produced larger grain; however, they were often more susceptible to stemborers, leaffolders (Cnaphalocrocis medinalis) and other caterpillars (Rivula atimeta). This was largely a consequence of hybrid heterosis for plant biomass and was strongly affected by crop duration. We make a series of recommendations to improve hybrid breeding to reduce the risks of herbivore damage.

In rice ecosystems, seeding densities can be adjusted to compensate for lower nitrogen levels that reduce GHG emissions, or to increase farm profitability. However, density-induced changes to plant anatomy could affect herbivore-rice interactions, and alter arthropod community dynamics. We conducted an experiment that varied transplanting density (low or high), nitrogenous fertilizer (0, 60 or 150 kg added ha−1) and rice variety (resistant or susceptible to phloem-feeding insects) over two rice-growing seasons. Yields per plot increased with added nitrogen, but were not affected by variety or transplanting density. Planthopper and leafhopper densities were lower on resistant rice and in high-density field plots. Nitrogen was associated with higher densities of planthoppers, but lower densities of leafhoppers per plot. High planting densities and high nitrogen also increased rodent damage. The structure of arthropod herbivore communities was largely determined by season and transplanting density. Furthermore, two abundant planthoppers (Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)) segregated to low and high-density plots, respectively. The structure of decomposer communities was determined by season and fertilizer regime; total decomposer abundance increased in high-nitrogen plots during the dry season. Predator community structure was determined by season and total prey abundance (including decomposers) with several spider species dominating in plots with high prey abundance during the wet season. Our results indicate how rice plasticity and arthropod biodiversity promote stability and resilience in rice ecosystems. We recommend that conservation biological control, which includes a reduction or elimination of insecticides, could be promoted to attain sustainable rice production systems. [ABSTRACT FROM AUTHOR]

In rice ecosystems, seeding densities can be adjusted to compensate for lower nitrogen levels that reduce GHG emissions, or to increase farm profitability. However, density-induced changes to plant anatomy could affect herbivore-rice interactions, and alter arthropod community dynamics. We conducted an experiment that varied transplanting density (low or high), nitrogenous fertilizer (0, 60 or 150 kg added ha−1) and rice variety (resistant or susceptible to phloem-feeding insects) over two rice-growing seasons. Yields per plot increased with added nitrogen, but were not affected by variety or transplanting density. Planthopper and leafhopper densities were lower on resistant rice and in high-density field plots. Nitrogen was associated with higher densities of planthoppers, but lower densities of leafhoppers per plot. High planting densities and high nitrogen also increased rodent damage. The structure of arthropod herbivore communities was largely determined by season and transplanting density. Furthermore, two abundant planthoppers (Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)) segregated to low and high-density plots, respectively. The structure of decomposer communities was determined by season and fertilizer regime; total decomposer abundance increased in high-nitrogen plots during the dry season. Predator community structure was determined by season and total prey abundance (including decomposers) with several spider species dominating in plots with high prey abundance during the wet season. Our results indicate how rice plasticity and arthropod biodiversity promote stability and resilience in rice ecosystems. We recommend that conservation biological control, which includes a reduction or elimination of insecticides, could be promoted to attain sustainable rice production systems.

Abstract Herbivory tolerance can offset the negative effects of herbivory on plants and plays an important role in both immigration and population establishment. Biomass reallocation is an important potential mechanism of herbivory tolerance. To understand how biomass allocation affects plant herbivory tolerance, it is necessary to distinguish the biomass allocations resulting from environmental gradients or plant growth. There is generally a tight balance between the amounts of biomass invested in different organs, which must be analyzed by means of an allometric model. The allometric exponent is not affected by individual growth and can reflect the changes in biomass allocation patterns of different parts. Therefore, the allometric exponent was chosen to study the relationship between biomass allocation pattern and herbivory tolerance. We selected four species (Wedelia chinensis, Wedelia trilobata, Merremia hederacea, and Mikania micrantha), two of which are invasive species and two of which are accompanying native species, and established three herbivory levels (0%, 25% and 50%) to compare differences in allometry. The biomass allocation in stems was negatively correlated with herbivory tolerance, while that in leaves was positively correlated with herbivory tolerance. Furthermore, the stability of the allometric exponent was related to tolerance, indicating that plants with the ability to maintain their biomass allocation patterns are more tolerant than those without this ability, and the tendency to allocate biomass to leaves rather than to stems or roots helps increase this tolerance. The allometric exponent was used to remove the effects of individual development on allocation pattern, allowing the relationship between biomass allocation and herbivory tolerance to be more accurately explored. This research used an allometric model to fit the nonlinear process of biomass partitioning during the growth and development of plants and provides a new understanding of the relationship between biomass allocation and herbivory tolerance.

Drought is a global threat, increasing in severity and frequency throughout tropical ecosystems. Although plants often face drought in conjunction with biotic stressors, such as herbivory or disease, experimental studies infrequently test the simultaneous effects of drought and biotic stress. Because multiple simultaneous stressors may have non‐additive and complex effects on plant performance, it is difficult to predict plant responses to multiple threats from research examining one stress at a time. Using an experimental approach in the greenhouse, we investigated potential non‐additivity in seedling growth and survival to simulated drought and herbivory across a phylogenetically diverse pool of ten Hawaiian plant species. Overall, seedlings showed limited tolerance, defined as similar growth and survival in stressed compared with control (non‐stressed) plants, to simulated herbivory and drought, with the combined effects of both stressors to be generally additive and negative across species. Significant variation in stress tolerance was detected among species, and species variation was explained, at least in part, by functional traits such that species with larger root/shoot ratios and smaller seeds, tended to demonstrate greater herbivory and drought tolerance. Future research incorporating additional trait analysis and different stressors could shed light on mechanisms underlying seedling stress tolerance and clarify whether additivity, as detected in this study, extends across other combinations of stressors. Such work will provide needed insights into the regeneration of seedlings in tropical forests under threats of herbivory and climate change. [ABSTRACT FROM AUTHOR]

Herbivory tolerance can offset the negative effects of herbivory on plants and plays an important role in both immigration and population establishment. Biomass reallocation is an important potential mechanism of herbivory tolerance. To understand how biomass allocation affects plant herbivory tolerance, it is necessary to distinguish the biomass allocations resulting from environmental gradients or plant growth. There is generally a tight balance between the amounts of biomass invested in different organs, which must be analyzed by means of an allometric model. The allometric exponent is not affected by individual growth and can reflect the changes in biomass allocation patterns of different parts. Therefore, the allometric exponent was chosen to study the relationship between biomass allocation pattern and herbivory tolerance. We selected four species (Wedelia chinensis, Wedelia trilobata, Merremia hederacea, and Mikania micrantha), two of which are invasive species and two of which are accompanying native species, and established three herbivory levels (0%, 25% and 50%) to compare differences in allometry. The biomass allocation in stems was negatively correlated with herbivory tolerance, while that in leaves was positively correlated with herbivory tolerance. Furthermore, the stability of the allometric exponent was related to tolerance, indicating that plants with the ability to maintain their biomass allocation patterns are more tolerant than those without this ability, and the tendency to allocate biomass to leaves rather than to stems or roots helps increase this tolerance. The allometric exponent was used to remove the effects of individual development on allocation pattern, allowing the relationship between biomass allocation and herbivory tolerance to be more accurately explored. This research used an allometric model to fit the nonlinear process of biomass partitioning during the growth and development of plants and provides a new understanding of the relationship between biomass allocation and herbivory tolerance. [ABSTRACT FROM AUTHOR]

Metal hyperaccumulation can increase plant resistance to herbivory, but tolerance as an herbivore defense has been little investigated. This study explored the interaction between Ni hyperaccumulation and herbivory tolerance using Streptanthus polygaloides. Plants were grown in one of two potting soil Ni treatments: Ni-amended (800 µg g−1 added Ni) or unamended (0 µg g−1 added Ni). One-month-old plants were arbitrarily assigned one of four levels of artificial herbivory damage applied to the leaves. Response variables included aboveground dry biomass and Ni concentration, total leaf number, final plant height, and total number of flowers, and were analyzed by two-way ANOVA. We found no consistent soil Ni effect, artificial herbivory effect, or interaction between soil Ni and artificial herbivory treatments for total leaf number or final plant height. However, there was a soil Ni effect for biomass, flower production, and Ni concentrations: all were greater for plants grown in Ni-amended soil when compared to plants grown in unamended soil. There was also a significant interaction between treatments for number of flowers produced (reflecting plant fitness) as well as for aboveground biomass. Plants of S. polygaloides receiving greater damage produced significantly more flowers, and had greater biomass, when grown in Ni-amended soil than plants in unamended soil. We conclude that Ni hyperaccumulation is associated with herbivory tolerance of S. polygaloides, increasing plant fitness when herbivory damage is severe. Herbivory tolerance provides an additional dimension to elemental defenses that can supplement the defense trait of herbivory resistance. [ABSTRACT FROM AUTHOR]

Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade‐tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and – at temperate latitudes – low temperatures. Although empirical studies show that shade‐tolerant species in tropical forests do allocate more photosynthate to storage than their light‐demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta‐analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability – and not temperature – limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late‐successional tree species may have been over‐estimated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tree saplings tolerated defoliation by bud activation. • New branch development allowed tree sapling aerial growth maintenance. • Defoliation decreased tree sampling height, diameter, and root growth. • Cattle grazing may retard juvenile recruitment into reproductive size classes. Livestock rearing is increasing in savannas, so the ability of trees to regrow after consumption represents one of the critical aspects of savanna structure and functioning. Here, we identified specific traits—which may explain the mechanisms behind defoliation tolerance—in saplings of two encroacher tree species (Vachellia caven and Vachellia aroma). We carried out common garden and field experiments where manual defoliation treatments simulated the cattle grazing regime employed in the study region. At the end of the experiments, we recorded growth variables and, in the common garden experiment, root reserves concentration. In the common garden, defoliation decreased height and basal diameter growth but did not affect the aerial relative growth rate. Also, defoliation increased the number of branches per plant and decreased root relative growth rate. Starch concentration was higher or similar in defoliated plants than controls, depending on the species. In the field, defoliation decreased both species' height and basal diameter growth. We found that tree saplings tolerated defoliation, and the mechanisms behind tolerance would be linked mainly to the axillary bud activation and not to storage reserve mobilization. Over time, these plant architectural changes might complicate cattle movement and management in these systems. From a long-term perspective, livestock rearing might retard juvenile recruitment into reproductive-size classes (e.g. , adults) by reducing overall tree growth rates. [ABSTRACT FROM AUTHOR]

En numerosas zonas el pastoreo extensivo se ha visto como una amenaza para la conservación de la vegetación. Sin embargo, los herbívoros tienen un papel fundamental en el mantenimiento de los ecosistemas y sus efectos sobre las comunidades vegetales son complejos y específicos para cada zona. Por tanto, es necesario estudiar el efecto de estos herbívoros sobre cada tipo de vegetación. En el presente trabajo se analiza la respuesta a corto plazo, de 2 especies de matorral (Bouvardia erecta y Justicia candicans), una de ellas en estado crítico de conservación, a la exclusión de ganado mediante cercados. Los resultados muestran que en tan sólo unos meses, las plantas protegidas dentro de los cercados presentaron una mayor cobertura que las situadas fuera. Sólo J. candicans muestra una disminución en la inversión reproductora, mientras que para B. erecta no se encontró variación en el esfuerzo reproductivo entre plantas ramoneadas y las no ramoneadas, lo cual sugiere que esta especie, en cierto grado, está adaptada a ser consumida. Si bien, será necesario un seguimiento a largo plazo para poder analizar posibles cambios en las poblaciones de estas especies, este trabajo nos muestra el cambio potencial que puede sufrir la vegetación ante la eliminación del ganado.In many areas of the planet extensive grazing has been considered as a limitation to the conservation of vegetation. However, herbivores have a fundamental role in maintaining ecosystems and their effects on plant communities are complex and specific. Therefore, studies that analyzed the effect of these herbivores on vegetation are needed. In this study we analyze the response, in the short time, of 2 species of shrubs, one of them in critical state of conservation, to the exclusion of livestock with 3 enclosures. The results show that, in just a few months, the plants included in the enclosures were greater (major canopy area) than plants outside enclosures. However, only one of them shows a decline in reproductive investment while for the other we did not found changes in reproductive effort between plants grazed and not grazed. So we can consider that this shrub species is, to some degree, adapted to be consumed. It will require a long-term monitoring to analyze possible changes in these species population in livestock exclusion areas. However, results showed the potential changes that may occur to vegetation after livestock removal.

In a small plot study we used a systematic additive design to evaluate at what severity and frequency of defoliation sideoats grama (Bouteloua curtipendula) would remain competitive and recover from defoliation while growing with meadow dropseed (Sporobolus compositus). In the 3-year study plants were transplanted from pots into the experimental design when equal in size. WhenB. curtipendulawas selectively defoliated moderately or severely, at both 30- and 60-day intervals, it still produced as much as when undefoliated growing with undefoliatedS. compositus. Moderately defoliatedB. curtipenduladid not reduce biomass yield ofS. compositusgrowing with it compared to whenS. composituswas growing alone. When both plants were non-selectively defoliated severely,S. compositusresponded very weakly andB. curtipendularecovered at the same rate as it had under the other defoliation treatments. The total biomass produced by both species growing together was highest whenB. curtipendulawas moderately defoliated. As soil moisture was not limited in this experiment we do not believe our results refute the hypothesis that selective grazing by livestock in these ecosystems has contributed to a reduction ofB. curtipendularelative toS. compositus. AlthoughS. composituswas reduced more thanB. curtipendulaby heavy nonselective defoliation this treatment is unlikely to produce desirable results in the long term as the highest total vegetation production occurred whenB. curtipendulawas moderately defoliated. [ABSTRACT FROM AUTHOR]

Abstract: Ground-layer vegetation of abandoned woodlands is threatened by excessive shading and increasing pressure from ungulate herbivores. Although these issues are studied separately, they are presumed to be interactive because decreasing energy input into ground layer seems to limit herbivory tolerance in plants. To separately estimate impacts of succession, herbivory, and their interactions, I conducted a 2-by-2 factorial experiment (creating canopy gaps, setting deer exclosures, their combinations and controls) in abandoned woodlands, where ground-layer vegetation had nearly vanished from deer herbivory. Changes of plant community were monitored three times since half a year before the start of experiment. Rapid increases in foliar cover, plant height, and species richness were found in plots under gaps within half a year from the beginning of the experiment. The major cause of this rapid increase was reestablishment of light-demanding and fast-growing species, whose compensation growth exceeded consumption by deer. In contrast, no significant change was found in ground-layer vegetation under a closed canopy, where only shade-tolerant and slow-growing species existed. These results suggested that limits in light resulting from the progress of forest succession is a primary factor inhibiting recovery of ground-layer vegetation from herbivory damage. In the short term, a combination of gap creation and the removal of herbivores is necessary to restore ground-layer plants in abandoned woodlands. [Copyright &y& Elsevier]

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Abstract: Rapid evolutionary changes in invasion-related ecological traits of alien plants are receiving considerable attention in current ecological research. Tolerance to herbivory is of particular interest because of the potential for using biological agents to control the spread of invasive plants. In this study, we compared herbivory tolerance in six populations of tall form Spartina alterniflora: three from its introduced range in Jiangsu Province, China, and three from its native range in Georgia, USA. Plants were grown in a greenhouse and subjected to a full-factorial experimental design with three simulated leaf herbivory levels and two levels of nitrogen availability for 20weeks. We found that native and invasive tall form S. alterniflora grown under different nitrogen conditions responded to simulated leaf herbivory differently with regard to underground and aboveground biomass and total culm height. Invasive S. alterniflora populations had a greater capacity to compensate for leaf damage than native populations in terms of underground biomass and aboveground biomass, particularly with low nitrogen availability. In addition, invasive S. alterniflora also showed higher compensatory capacity than native plants with regard to total culm height in both nitrogen treatments and with regard to tiller number in the high nitrogen treatment. Elevated nitrogen availability significantly increased the compensatory capacity of underground biomass in native S. alterniflora populations but did not affect any factor in invasive populations. Our results suggested a rapid evolutionary change in herbivory tolerance of invasive tall form S. alterniflora after its introduction to China. Understanding such changes in the tolerance to herbivory between native and invasive populations of alien plants has important implications for improving management efficiency. [Copyright &y& Elsevier]

A positive effect of herbivory on plant reproduction (overcompensation) has been documented mostly in monocarpic plants. Iteroparous perennials can be used to test whether enhanced reproduction in 1 year has negative future consequences as predicted by optimal allocation models. This study was intended to verify this prediction in the iteroparous herb Sedum maximum, applying mechanically simulated herbivory. I monitored 132 labelled S. maximum individuals during 2 years of study. They were randomly assigned to two groups: clipped and control. Infructescence dry mass, total seed dry mass, seed size, germination rate and an increase of root dry mass during the season were assessed in the experimental plants. Since only roots can survive to the next season, root dry mass was considered a reliable measure of allocation to future performance. Clipped plants showed increased fruit and seed dry mass versus the controls, with no other aspect of reproduction affected. Apical bud removal also had a positive effect on increase of root dry mass. The results indicate true overcompensation in response to simulated herbivory with no future costs of increased reproduction. Moreover, increased plant reproduction as a result of herbivory is likely to persist in the following years: clipping increased not only seed production but also root growth. This response is inconsistent with the results of optimal allocation models and the discrepancy is probably due to violation of the resource limitation assumption. Plants adapted to tolerate herbivory seem not to reproduce at the maximum rate when undamaged, but rather withhold resources to be allocated to reproduction after herbivory. [ABSTRACT FROM AUTHOR]

The activation of dormant meristems following apical damage is an important mechanism for tolerance of herbivore damage, but its impact could vary with resource availability. Here, we examined central predictions of the limiting resource model (LRM), according to which high resource availability can support damage tolerance in plants with deterministic apical dominance, but will have limited or no effect in plants that are induced to increase branching by increased resource availability regardless of damage. We examined these predictions by studying the branching patterns of Medicago truncatula plants in response to both light and water availabilities and their effects on tolerance of apical damage. We used plants from environments that were predicted to select for different levels of apical dominance. Intact plants from the more productive and competitive population exhibited strong apical dominance and refrained from branching even under full light, whereas plants from the less productive and sparser population exhibited greater plasticity in apical dominance and readily branched under high water and light. In accordance with the LRM, these differences translated into differential responsiveness to apical damage: given abundant water, apical damage induced the activation of lateral meristems and increased pod and seed production in plants from the more productive environment, but not in plants from the less productive environment. These results suggest an adaptive association between deterministic inhibition of lateral meristems and compensatory ability, which supports the hypothesis that greater compensatory responsiveness to apical damage could be a derivative of adaptation to other environmental stresses, such as light competition. [ABSTRACT FROM AUTHOR]

The article presents a case study which identifies the anti-herbivore traits in agricultural plants. The study involves the role of trichomes against a sap-feeding insect, the leafhopper, on potato. It also explores two different types of costs, the allocation costs focusing on the relationship of trichomes and yield, and the costs that involve trade-offs with alternative strategies.

Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera ( Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a ‘fast grower’, Vitis berlandieri × Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia × Vitis rupestris cv. 101–14 Mgt). Each root system was grafted with a genetically identical shoot system ( Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects. [ABSTRACT FROM AUTHOR]

Root proliferation of desirable (Stipa clarazii and S. tenuis) and undesirable (S. ambigua) perennial grasses was studied in semiarid rangelands of Central Argentina (40°39′S, 62°54′W) in 1998. On 17 September, soil cores were removed from the edge of the plant, metal structures lined with screen mesh (hereafter called bags) were buried in the holes, and root-free soil was placed into these structures. Numbers of green tillers and circumference per plant had previously been determined. Since plants were of unequal size among species, root length and root dry weight data are reported on a per green tiller basis. Half of the plants was defoliated to 5 cm stubble height on 17 September and/or 12 October, while the other half remained undefoliated (controls). Bags were destructively harvested either 20 days after the first defoliation (first sampling) or 56 days after the second defoliation (second sampling) by digging out soil very carefully around each bag. Roots were washed from soil, root length estimated by the line intercept method, root dry weight determined after oven-drying, and root length per unit root dry weight calculated from the two measured variables. Root length and dry weight were more than 96% greater on defoliated and undefoliated plants of S. clarazii than on those of S. tenuis or S. ambigua for both sampling dates. Root length per unit root dry weight, however, was more than 43% greater (p < 0.05) in S. tenuis than in S. clarazii and S. ambigua during the second sampling. Defoliated plants had a similar root length and root dry weight than undefoliated plants in all three species, although plants of S. tenuis defoliated twice showed a greater (p < 0.05) root length than undefoliated controls. Root length and root dry weight were similar between sampling periods, except on undefoliated plants of S. tenuis which had a greater (p < 0.05) root length and root dry weight at the first than at the second sampling. Although root length per unit root dry weight may be greater in S. tenuis than in S. clarazii and S. ambigua, greater root length and dry weight increases in S. clarazii after defoliation appear determinant in contributing to explain its greater competitive ability and defoliation tolerance when compared with the other two species. Nomenclature of taxa followed . [ABSTRACT FROM AUTHOR]

Summary: The introduced tree, Sapium sebiferum, is a serious invader throughout the southeastern United States. Low herbivore loads, commonly attributed to high herbivore resistance, are assumed to give Sapium a competitive advantage over native vegetation. Because herbivory resistance is considered energetically expensive, we predicted that if Sapium experienced higher levels of damage its growth would significantly decrease. We examined the effects of different levels of simulated leaf herbivory on the growth of Sapium and Celtis laevigata, a native tree, at three levels of nitrogen and three levels of light availability. Potted seedlings were grown in a complete factorial design. Stem height growth rate, diameter growth rate and plant mass of both Sapium and Celtis were significantly affected by shade and nitrogen treatments. Nitrogen increased the growth of both species and seedlings in shaded conditions grew larger than those in ambient sunlight. Simulated leaf herbivory had a significantly negative impact on diameter growth rate and plant mass of Celtis. Surprisingly, neither Sapium height growth rate, diameter growth rate, nor any measure of plant mass were significantly affected by simulated leaf herbivory. Rather, Sapium exhibited considerable phenotypic plasticity and was able to compensate for leaf damage in all resource conditions. Our findings suggest herbivory tolerance is a previously unappreciated trait of Sapium that, in conjunction with phenotypic plasticity and low levels of herbivory in its introduced range, likely contributes to its invasiveness. Der eingeführte Baum, Sapium sebiferum, ist ein bedeutender Einwanderer in den gesamten südöstlichen Vereinigten Staaten. Es wird angenommen, dass eine geringe Herbivoren-Belastung Sapium einen Konkurrenzvorteil gegenüber der einheimischen Vegetation verschafft, die im Allgemeinen der hohen Herbivoren-Resistenz zugeschrieben wird. Weil Herbivoren-Resistenz als energetisch aufwändig betrachtet wird, sagten wir voraus, dass das Wachstum signifikant abnimmt, wenn Sapium einen höheren Grad der Beschädigung erfährt. Wir untersuchten die Auswirkungen unterschiedlicher Grade simulierter Herbivorie auf das Wachstum von Sapium und Celtis laevigata, einem einheimischen Baum, bei drei Niveaus der Stickstoff- und drei Niveaus der Lichtverfügbarkeit. Eingetopfte Keimlinge wurden in einem durchgehend faktoriellen Design kultiviert. Die Wachstumsraten der Stammhöhe und des Durchmessers sowie die Pflanzenmasse wurden bei Sapium und Celtis signifikant durch die Schatten- und Stickstoffbehandlungen beeinflusst. Stickstoff erhöhte das Wachstum bei beiden Arten und die Keimlinge wuchsen unter Schattenbedingungen höher als bei vollem Sonnenlicht. Simulierte Blattherbivorie hatte bei Celtis eine signifikant negative Einwirkung auf die Durchmesser-Wachstumsrate und die Pflanzenmasse. éberraschenderweise wurden bei Sapium weder die Höhen- und Durchmesser-Wachstumsrate, noch irgendein ein Maß für die Pflanzenmasse durch die simulierte Blattherbivorie signifikant beeinflusst. Stattdessen zeigte Sapium eine beachtliche phänotypische Plastizität und war in der Lage Blattbeschädigungen unter allen Ressourcen-Bedingungen zu kompensieren. Unsere Ergebnisse legen nahe, dass Herbivorietoleranz ein bisher nicht beachtetes Merkmal von Sapium ist, das wahrscheinlich in Verbindung mit der phänotypischen Plastizität und den geringen Graden der Herbivorie im neuen Verbreitungsgebiet zu seiner Invasivität beiträgt. [Copyright &y& Elsevier]

We evaluated herbivory tolerance and competitive ability within twodominant : subordinate pairs of C4, perennial grasses at each of twosites to determine the contribution of these processes to herbivore-inducedspecies replacement. Herbivory tolerance was assessed by cumulative regrowthfrom defoliated plants of each species and competitive ability was evaluated byrelative uptake of a 15N isotope placed into the soil between pairedspecies in the field. Herbivory tolerance was similar for the dominant andsubordinate species in both plant pairs and defoliation intensity had a greaterinfluence on herbivory tolerance than did defoliation pattern. Both specieswithin the Sorghastrum nutans : Schizachyriumscoparium pairs exhibited comparable nitrogen acquisition from a15N enriched pulse with or without defoliation. In contrast, S. scoparium acquired more 15N than did itssubordinate neighbor, Bothriochloa laguroides when thisspecies pair was undefoliated. Uniform defoliation of this species pair at adefoliation intensity removing 70% of the shoot mass accentuated this responsefurther demonstrating the greater competitive ability of the dominant comparedto the subordinate species. Although the 90% defoliation intensity reducednitrogen acquisition by the dominant relative to the subordinate species, B. laguroides, it did not reduce nitrogen acquisition bythe dominant below that of the subordinate neighbor. The occurrence of similarherbivory tolerance among dominant and subordinate species indicates thatselective herbivory suppressed the greater competitive ability, rather than thegreater herbivory tolerance, of the dominant grasses in this experimentaldesign. These data suggest that interspecific competitive ability may be ofequal or greater importance than herbivory tolerance in mediatingherbivore-induced species replacement in mesic grasslands and savannas. [ABSTRACT FROM AUTHOR]

Inherent relative growth rate has been suggested as a major determinant of plant species' capacity to regrow and compensate for tissues lost to herbivores. We investigated: 1) the relationship between compensatory growth capacity and relative growth rate (RGR) in six semiarid-land shrubs following removal in winter or spring of 90% of the previous year's growth, 2) the influence of loss of buds on production of new growth and 3) the relationship between meristematic potential and the capacity to produce new growth in four of the six semiarid-land shrub species. Four-year-old plants growing under field conditions were used in the study. The species with the highest inherent growth rate, sagebrush [ Artemisia tridentata ssp. vaseyana (Rydb.) Beetle], died following the severe clipping treatments. The other five species exactly compensated for lost tissues. Inherent growth rates and compensatory growth capacity of the shrubs were not correlated. Loss of 90% of the buds on the previous year's growth did not limit production of new growth. Instead, shrubs that lost buds produced more new growth biomass than the controls. The shrub species had significantly different meristematic potential. Curlleaf mountain mahogany ( Cercocarpus ledifolius Nutt.) and serviceberry ( Amelanchier alnifolia Nutt.) had the greatest and least number of buds and long shoots per plant, respectively. The number of long shoots produced following bud removal was positively correlated with new growth biomass, while the percentage of long shoots produced at the basal position on twigs was negatively correlated with new growth biomass. Our results suggest that inherent growth rate is not likely to influence production of new growth following browsing when resources for growth are not limiting. In contrast, the ability of a shrub to initiate long shoot growth is likely to influence production of new growth even when resources for growth are abundant. [ABSTRACT FROM AUTHOR]

The ability of plants to rapidly replace photosynthetic tissues following defoliation represents a resistance strategy referred to as herbivory tolerance. Rapid reprioritization of carbon allocation to regrowing shoots at the expense of roots following defoliation is a widely documented tolerance mechanism. An experiment was conducted in a controlled environment to test the hypothesis that herbivory-sensitive perennial grasses display less flexibility in reprioritizing carbon allocation in response to defoliation than do grasses possessing greater herbivory tolerance. An equivalent proportion of shoot biomass (60% dry weight) was removed from two C perennial grasses recognized as herbivory-sensitive, Andropogon gerardii and Schizachyrium scoparium, and two C perennial grasses recognized as herbivory-tolerant, Aristida purpurea and Bouteloua rigidiseta. Both defoliated and undefoliated plants were exposed to CO for 30 min, five plants per species were harvested at 6, 72 and 168 h following labeling, and biomass was analyzed by isotope ratio mass spectrometry. The tallgrass, A. geraiddii, exhibited inflexible allocation priorities while the shortgrass, B. rigidiseta, exhibited flexible allocation priorities in response to defoliation which corresponded with their initial designations as herbivory-sensitive and herbivory-tolerant species, respectively. A. gerardii had the greatest percentage and concentration of C within roots and lowest percentage of C within regrowth of the four species evaluated. In contrast, B. rigidiseta had a greater percentage of C within regrowth than did A. gerardii, the greatest percentage of C within new leaves of defoliated plants, and the lowest concentration of C within roots follwing defoliation. Although both midgrasses, S. scoparium and A. purpurea, demonstrated flexible allocation priorities in response to defoliation, they were counter to those stated in the initial hypothesis. The concentration of C within new leaves of S. scoparium increased in response to a single defoliation while the percentage and concentration of C within roots was reduced. A. purpurea was the only species in which the percentate of C within new leaves decreased while the percentage of C within roots increased following defoliation. The most plausible alternative hypothesis to explain the inconsistency between the demonstrated responsiveness of allocation priorities to defoliation and the recognized herbivory resistance of S. scoparium and A. purpurea is that the relative ability of these species to avoid herbivory may make an equal or greater contribution to their overall herbivory resistance than does herbivory tolerance. Selective herbivory may contribute to S. scoparium's designation as a herbivorysensitive species even though it possesses flexible allocation priorities in response to defoliation. Alternatively, the recognized herbivory resistance of A. purpurea may be a consequence of infrequent and/or lenient herbivory associated with the expression of avoidance mechanisms, rather than the expression of tolerance mechanisms. A greater understanding of the relative contribution of tolerance and avoidance strategies of herbivory resistance are required to accurately interpret how herbivory influences plant function, competitive interactions, and species abundance in grazed communities. [ABSTRACT FROM AUTHOR]

• Tolerance to herbivory influences the success of invasive species in introduced ranges. • We tested differences in tolerance between the invasive Alternanthera philoxeroides and its native congener A. sessilis. • Alternanthera philoxeroides exhibited a greater tolerance to herbivory than A. sessilis , via resource allocation to roots. • Our study highlights the importance of resource allocation for the successful invasion of A. philoxeroides. Tolerance to herbivory influences the success of invasive species in introduced ranges, and thus a comparison of the difference in herbivory tolerance between invasive and native species may help to understand the mechanisms of plant invasions. We conducted a greenhouse experiment in Beijing, China to examine effects of aboveground herbivory (by a beetle Agasicles hygrophila or not) and nitrogen availability (high vs. low) on growth and physiology of the invasive plant Alternanthera philoxeroides and its coexisting native congener A. sessilis. Herbivory by A. hygrophila significantly reduced total mass and aboveground development of both plant species, and the negative effects of herbivory on leaf mass, ramet number, and leaf number were more remarkable at the high than at the low nitrogen level. On the other hand, herbivory did not affect root mass and even increased root to shoot ratio of both plant species. The increase in root to shoot ratio and relative ratio of root mass caused by herbivory was also stronger in A. philoxeroides than in A. sessilis. Besides, herbivory exerted neutral or positive effects on the concentrations of starch and total non-structural carbohydrates in stems and roots of A. philoxeroides , but negative effects on the physiological measures of A. sessilis. We conclude that A. philoxeroides may possess a stronger tolerance to herbivory than A. sessilis and that increased resource allocation to roots could potentially contribute to compensatory responses of A. philoxeroides to aboveground herbivory. Our findings also suggest that the control of A. hygrophila may be invalid in belowground invasion of A. philoxeroides , and that belowground herbivores should be considered in the future management of invasive species. [ABSTRACT FROM AUTHOR]